Re: C vs C++

Mark, frankly speaking packed decimal was my suspect since I saw the
difference. I saw the difference - it was intuitively clear that the
implementations of packed decimal is fundamentally different in C and C++
(however unclear why). What I'll do tomorrow, I'll write my own trivial
benchmark using decimal arithmetics.
Hopefully I shall see the difference.
The program uses decimal (15,0), decimal (15,9) and decimal (11,7) - It
seems that they all fit into 8 byte int.
I'll then see which is better - staying on C and decimals or switch to C++
and integers...

Thanks,
Jevgeni.
 On Feb 16, 2015 8:29 PM, "Mark S Waterbury" <[email protected]>
wrote:

> Jevjeni:
>
> I just noticed near the bottom of your post, where you said:
>
>         Program makes a lot of calculations with packed decimal.
>
> There is a big difference in the way ILE C implements support for "packed
> decimal" as a "native" data type -- versus the way it is "supported" in ILE
> C++ -- in ILE C, the compiler directly genrerates in-line code (in WCode /
> NMI)  to work on packed decimal data.  In the ILE C++ compiler, support for
> "packed decimal" is through a C++ library called "BCD" -- there are a lot
> of macros and such defined in the QSYSINC/H include member named BCD ... if
> you take a peek at that member, I think you will see that this uses
> "operator overloading" in C++ to trick the compiler into calling the
> desired library functions when operations are performed on "packed decimal"
> data.
>
> This difference could easily account for the big differences you are
> seeing.
>
> And then, you said:
>
>         ... is there anything that can be done about it?
>
> In C++, you could look into converting the packed decimal data into 64-bit
> integers, and then performing any calculations using those long integers.
> This would be much faster than using packed decimal arithmetic, then
> convert back to packed decimal format, if needed.  Or, just stick with ILE
> C/400 for those programs that require doing a lot of packed decimal
> arithmetic operations.
>
> Hope that helps,
>
> Mark S. Waterbury
>
> > On 2/16/2015 9:56 AM, Jevgeni Astanovski wrote:
>
>> Hi all.
>> Does anyone have any idea why C++ program is significantly slower than
>> C program?
>>
>> Explain the situation.
>> I have a number of API-s that are called via RPC, access some tables,
>> make some calculations and return some structures to the caller.
>> They've all been written on ILE/C.
>> Recently I started to experiment with porting them to ILE/C++. There
>> was a number of reasons why it would be nice.
>> After I rewrote the first one, I started to measure performance. This
>> is an issue for me as some of them are called hundreds of thousands
>> times per day.
>> Found out that it is approximately 2 times slower than C version.
>> Shared a code to colleges - no one found anything suspicious. However
>> one guy came out with a "brilliant" idea - he advised me to try to
>> recompile my C program with CPP compiler and see the performance.
>> Guess what? C program compiled with CPP compiler was the same 2 times
>> slower than C program compiled with C compiler....
>>
>> And the only modifications that I did for compiling C with CPP compiler
>> was:
>> 1. Substituted "#pragma mapinc" table structue definitions with those
>> generated by GENCSRC;
>> 2. Changed char and unsigned char in a couple of places as C++ is more
>> strict;
>> 3. Made a substitution for "NNNND" constants (like 100D for example)
>> as C++ does not support that.
>>
>> What I saw is that time increase looks like it has a proportional nature.
>> I tested API in 3 cases (number of tests is over 100): simple request,
>> medium request; complicated request and the timing is:
>> Simple C: 1ms; Simple C++ : 2ms
>> Medium C: 3ms; Simple C++ : 7ms
>> Long C: 25ms; Long C++: 60ms.
>>
>> The difference is in number of records read from table and a number of
>> calculations.
>> That is a simple one retrieves less that 10 records; medium - more
>> than 10 and long - more than 100. Program makes a lot of calculations
>> with packed decimal.
>>
>> Any idea why it is like that and is there anything that can be done about
>> it?
>>
>> Thanks in advance,
>>
>> Jevgeni.
>>
>
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